This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. Section 119 from an application for xe2x80x9cGAIN CONTROL DEVICE AND METHOD FOR ERBIUM DOPED FIBER AMPLIFIER,xe2x80x9d filed earlier in the Korean Industrial Property Office on Sep. 6, 2000, and there duly assigned Ser. No. 52684/2000.
1. Field of the Invention
The present invention relates to an erbium doped fiber amplifier, and more particularly to a gain control device and method for an erbium doped fiber amplifier.
2. Description of the Related Art
Conventional erbium doped fiber amplifiers (EDFAs) would experience gain transients with the deletion or addition of one or more channels. In order to correct degradation in the system""s bit error rate, a gain control device is required to automatically maintain a constant gain among channels when the number of input channels and the intensity variation of input signal light changes. Although optical gain control is effective in an erbium doped fiber amplifier, problems arise that are associated with complexity in the structure of the erbium doped fiber amplifier and a condition variation depending on the position of the erbium doped fiber amplifier.
Another method uses the adjustment of pumping light by controlling the bias current supplied to the source of the pumping light. However, when this method is applied to a wavelength division multiplexing system in which the number of channels in an optical signal may be variable, it is difficult to control the intensity of pumping light using a simple analog circuit as the intensity of the optical signal exhibit variable characteristics. Furthermore, the above gain control method requires the suppression of the temporal transient phenomenon occurring at the output optical signal due to an increase/decrease in the number of channels. Therefore, there is a need in the art for controlling gain in optical fiber amplifiers that solve the problems indicated above.
The present invention is directed to a gain control device and method for an erbium doped fiber amplifier, which is suitable for a wavelength division multiplexing system and capable of maintaining a constant gain irrespective of the intensity variation of optical signals.
The invention provides a gain control device and method for an erbium doped fiber amplifier, which is capable of suppressing a temporal transient phenomenon occurring at the output optical signal.
In accordance with one aspect, the present invention provides a gain control device for an erbium doped fiber amplifier adapted to amplify an input optical signal in accordance with an induced discharge of erbium ions. The gain control device includes:
a pumping light source for outputting pumping light adapted to excite the erbium ions while detecting a part of the pumping light, thereby outputting a pumping light sensing signal indicative of the power of the pumping light;
a photo-detecting unit for partially detecting the optical signal inputted to the erbium doped fiber amplifier, thereby outputting an input light sensing signal indicative of the power of the input optical signal;
a control unit for reading out from a look-up table a reference power corresponding to the optical signal power indicated by the input light sensing signal and for outputting a reference signal indicative of the read-out reference power;
an automatic gain control circuit for conducting a comparison between the reference power and the pumping light power based on the pumping light sensing signal and the reference signal, and for outputting a power compensating signal adapted to compensate for the difference between the reference power and the pumping light power; and,
a pumping light source driving unit for controlling the level of a bias current supplied to the pumping light source based on the power compensating signal.
In accordance with another aspect, the present invention provides a gain control method for an erbium doped fiber amplifier adapted to amplify an input optical signal in accordance with an induced discharge of erbium ions, wherein the erbium doped fiber amplifier includes a pumping light source for outputting pumping light adapted to excite the erbium ions, and a pumping light source driving unit for applying a bias current to the pumping light source. The method includes:
deriving the number of channels in the optical signal inputted to the erbium doped fiber amplifier from the input optical signal power;
if the derived channel number is different from a reference number of channels, outputting a temporal transient suppressing signal adapted to compensate for the difference between the derived channel number and the reference channel number to the pumping light source unit;
reading out a reference power corresponding to the power of the input optical signal from a look-up table;
comparing the power of the pumping light with the read-out reference power, thereby deriving the difference between the pumping light power and the reference power; and,
outputting a power compensating signal adapted to compensate for the power difference to the pumping light source driving unit.